The present invention relates to memory devices, and more particularly, to sense amplifiers for memory devices.
A typical memory device includes means for storing binary data (in case of a DRAM, a capacitor), word lines for accessing the storage means, and a bit line for inputting/outputting data. A sense amplifier is typically utilized for amplifying and transforming data on a bit line to a binary logic signal.
Conventionally, to read data stored in a memory cell, at first a pair of bit lines (i.e., a bit line and a bit bar line) are equalized. Data stored in a specific memory cell is coupled to a bit line so that a small voltage difference may occur between the bit lines. The sense amplifier senses the small voltage difference between the bit lines and amplifies the same to generate a binary signal.
FIG. 1 is an equivalent circuit diagram of a conventional sense amplifier 10. A bit line BL and a bit bar line /BL are connected to the sense amplifier 10 to comprise two input terminals SI and /SI. The sense amplifier 10 senses a voltage difference between the bit line BL and the bit bar line /BL, i.e., a voltage difference ΔV (about 25-30 mV) between the two input terminals, and then amplifies the difference to produce a binary logic signal at output terminals SO and /SO.
A typical conventional sense amplifier comprises an NMOS transistor and a PMOS transistor. However, as minimum feature size decreases, the size of sense amplifiers generally has decreased. Consequently, efficiency of sense amplifiers has become highly susceptible to a change of fabrication processes. For example, it may be assumed that a transistor used in a sense amplifier has a channel length of 3000 Å. If a gate dimension varies by only 150 Å, the transistor threshold voltage can change 30 mV. This may mean that the sense amplifier cannot sense a voltage difference less than 30 mV, that is, if the voltage difference between the bit line BL and the bit bar line /BL becomes less than 30 mV, the sense amplifier may not be able to sense the difference.
Accordingly, when a conventional sense amplifier configuration is used, it can be difficult to achieve a high degree of integration in a memory device. In addition, performance of the sense amplifier may be easily affected by a change of fabrication processes.